It is well known to provide liquid fabric softening compositions that soften treated fabric. Such compositions are typically added to fabric in the rinse cycle of the wash process. It has been observed that consumer preference is for liquid fabric conditioners that appear thick and creamy, cued by having a high viscosity and a high opacity. Conditioners that appear thin and/or translucent/watery may be perceived as being cheap and ineffective, whereas conditioners that appear thick and creamy are perceived as premium products. One route to achieve this is through the use of polymeric viscosity modifiers.
Fabric conditioners comprising polymeric viscosity modifiers and cationic softening agent are known in the art. For example, WO-A1-02/081611 discloses a fabric softener composition for the treatment of textile fibre materials in domestic applications comprises a fabric softener and a water-soluble polyurethane obtainable by reaction of (a) a diisocyanate, with (b) a polyether containing at least one hydroxyl group, (c) optionally a diol derived from an aliphatic residue having from 2 to 12 carbon atoms, and (d) an agent introducing a water-solubilising group.
US 2004/0214736, U.S. Pat. No. 6,827,795, EP0501714, US 2003/0104964 and U.S. Pat. No. 5,880,084 disclose fabric softening compositions comprising Polyquaternium 24 which is a polymeric quaternary ammonium salt of hydroxyethyl cellulose reacted with lauryl dimethyl ammonium epoxide.
EP-A2-0385749 discloses fabric conditioning compositions comprising a quaternary ammonium softening material and a polymeric thickener. The thickener has a hydrophilic backbone and two hydrophobic groups attached thereto.
EP 331237 discloses an aqueous fabric conditioning composition comprising a fabric softener and a non-ionic cellulose ether, characterised in that said non-ionic cellulose ether has a sufficient degree of non-ionic substitution selected from the class consisting of methyl, hydroxyethyl and hydroxypropyl to cause it to be water-soluble and wherein said non-ionic cellulose ether is hydrophobically modified by further substitution with one or more hydrocarbon radicals having abut 10 to 24 carbon atoms, in an amount between 0.2% by weight and the amount which renders the cellulose ether less than 1% by weight soluble on water at 20° C. Preferred non-ionic cellulose ethers are hydrophobically modified hydroxyethyl cellulose (HMHEC) commercially available from Hercules Incorporated under the trade designation “Natrosol Plus”. Specific examples of HMHEC which have been disclosed in fabric conditioning compositions are Natrosol Plus 330 and Natrosol Plus 331.
HMHEC polymers achieve viscosity build up by forming links between dispersed particles of the fabric conditioner system i.e. they act as “associative thickener”. This is in contrast to “continuous phase thickeners” which work simply by thickening the continuous phase without any association. The benefits of HMHEC's are that they are more weight effective and hence are a more cost effective solution to achieving high product viscosities and also reduces material consumption i.e. better for the environment generally.
Where these polymers have been used previously with dilute products these have generally proven to be most effective at moderate temperatures (<37° C.) with softener actives that contain predominantly dialkyl cationic species. At higher temperatures the viscosity tends to decrease significantly before the compositions gel due to hydrolysis. This is disadvantageous especially if the target viscosity is relatively high.
In order to maintain the product viscosity, the HMHEC must remain associated or “bound” to the dispersed phase. If the polymer loses this binding, the hydrophobic moieties of the polymer can associate intramolecularly such that the viscosity drops below specification and the product becomes thin and more liable to separation. Another key issue regarding TEAQ type actives is that these actives may contain a significant amount of more water soluble mono-ester components. These components become even more water soluble as the temperature of the system is raised and this is believed to lead to the formation of micellar type structures in the continuous phase. These micelles are believed to facilitate the release of the hydrophobic chains of the polymer from the bilayer of the dispersed organic phase. In addition, as the ester linked actives hydrolyse under these high temperature conditions, the more hydrophobic triester and diester species break down to form the mono-ester products, thus exacerbating the problem even further.
The invention has been made with the above points in mind.